Conventionally, an image sensor which has a sensor array for performing photoelectric conversion, an imaging element for imaging light coming from a document on the sensor array, and a light source for illuminating the document is known.
FIG. 12 is a schematic perspective view showing the outer appearance of the conventional image sensor. Referring to FIG. 12, reference numeral 1 denotes a frame as a support member; and 5, a top plate glass which can contact a document PP and serves as a transparent member that specifies the read surface. Reference numeral 8 denotes spacers which contact the transparent member 5 to define the position of the sensor with respect to the read position. Most photosensors (pixels) line up in a main scan direction DM that agrees with the longitudinal direction of the frame 1, the widthwise direction of which agrees with a sub-scan direction DS.
FIG. 13 shows a section taken along a lone C-C′ in FIG. 12. Referring to FIG. 13, an imaging element 7 is set in a space D of the frame 1. A light source 6 is set in a space E. A sensor array 3 is arranged on an electric circuit board 4, and is set to face a space F. The spaces D, E, and F communicate with one another. Other spaces L and M are unfilled spaces which are formed upon forming the frame 1 by solid molding to prevent sink marks.
FIG. 14 is a sectional view showing other unfilled spaces of the conventional image sensor. In FIG. 14, spaces N, Q, R, and S are unfilled spaces.
Such image sensor is assembled as follows. That is, the light source 6 is fixed to a mount surface G of the frame 1 by an adhesive or screws, and the imaging element 7 is inserted into the space D and is fixed to a mount surface H of the frame 1 by an adhesive or screws. Then, the electric circuit board 4 provided with the sensor array 3 is fixed to a mount surface I of the frame 1 by an adhesive or screws.
However, in order to achieve still higher read resolution of the conventional image sensor, the following technical problems remain unsolved.
1. The flatness precision of a document and the image sensor is important to realize higher read resolution. However, it is hard for conventional molding of the frame 1, which is formed to have an unfilled shape that forms large openings on its outer surface, to obtain a frame thickness that can assure good molding balance with the flatness. Furthermore, since space L- and M-side blocks, which are partitioned by the space D as the optical path of optical information coming from the document PP, suffer variations in frame thickness, such variations in thickness of the frame 1 cause molding shrinkage variations. For these reasons, formation of a high-precision flat surface required for the frame 1 is limited, and it is difficult to form a high-precision flat surface having flatness of 0.1 mm or less over the total length of the image sensor in the main scan direction DM.
2. In order to realize higher read resolution, the frame 1 must have high rigidity so that it does not deform by a pressure T of a pressing means which prevents the image sensor or document PP from floating. However, upon conventional molding of the frame 1 which is formed to have an unfilled shape that forms large openings on its outer surface, the openings readily collapse, and the rigidity obtained with the frame 1 is limited.